After first saying it wouldn't respond, the United States has now denied it had anything to do with the Wednesday bombing death of an Iranian nuclear scientist. Surprising no one, Iran blamed the United States and Israel for the attack on Mostafa Roshan, who on Wednesday became the fourth Iranian nuclear scientist to die in a bomb attack in two years. From the Associated Press: "White House spokesman Tommy Vietor said the U.S. 'had absolutely nothing to do' with Mostafa Ahmadi Roshan's death. Vietor said the U.S. condemns 'all acts of violence, including acts of violence like what is being reported today.' " But someone's clearly out to get Iran's nuclear scientists. And we're sure the U.S. won't mind if they succeed.